1. Field of the Invention
This invention relates to an apparatus for transferring and shaping rubber sheet material, and more particularly to an apparatus for automatically and accurately applying on a forming drum a sheet-like rubber material like carcass ply and a breaker belt which are generally used as component parts in tire building.
2. Description of the Prior Art
In the tire building process, sheet-like rubber materials such as carcass plies a breaker belt, which are usually stored in the form of rolls on a feeder called a servicer, have thus far been manually applied around a forming drum by an operator, also manually cutting and ending the wrapped sheet material. Namely, the conventional servicer has been used only for the purpose of stocking tire building material, with no function of forcibly feeding the material to the tire building machine, so that it has been the conventional practice to draw out the material by the rotational force of the forming drum, resulting in inaccurate centering of the material. Therefore, the accuracy of the operation of applying a sheet-like rubber material around the forming drum as well as the corresponding productivity largely depended upon the manual skill, suffering from irregularities in the forming accuracy, which have adverse effects on the uniformity of the tires to be ultimately obtained, especially such irregularities that are detrimental in the case of radial tires.
In order to solve the problems of productivity and accuracy, there has been an urgent demand for an automatic tire forming machine which is equipped with an automatic cutter for cutting the feed material into strips of a predetermined length. In order to ensure that a strip of rubber sheet 1, which has been cut into a predetermined length, be fed to a forming drum 2 in an accurately centered state in an automatic tire building servicer, difficulty has been encountered in restricting sideward positional deviations of an acute triangular portion at the tail end of a rubber strip 3 as shown in FIG. 5 in a case where the cutting line forms large angles .theta. with the a line extending transversely of the rubber strip 3. Namely, since it is difficult to restrict inward deviations by means of rows of conventional guide rollers 4, it is desirable to hold the rubber sheet 3 in a centered position prior to the cutting operation and to feed the rubber sheet of a predetermined length to a shaping drum 2, keeping the centered position. In this connection, there has been proposed a tire building servicer of the type which employs a belt conveyer as means for transferring the material onto the surface of the forming drum, keeping the material on the conveyer completely free of slipping. A typical servicer of this type is shown in FIG. 4. However, they have not yet reached the stage of actual application due to the problems as stated below.
(1) The material which is fed to the forming drum 2 from a stock roll of material 5 is in the form of a series of cut strips 6 of a predetermined length which have to be separated from each other in the course of transfer by a plurality of belt conveyers 7 and 8 and therefore are susceptible to positional deviations as they are freed from the conveyer surface for passage through a bridge 9 across a gap between the two belt conveyers 7 and 8.
(2) Each cut 6 of a predetermined length is separated at the bridge 9 between the belt conveyers 7 and 8. In a case where the cutting line of a breaker belt or the like is disposed at large angles .theta. with the transverse direction of the material, it becomes necessary to provide a longer bridge between the belt conveyers 7 and 8 to prevent slipping of the transferred material which may occur at the time of separation. In such a case, the feed material is susceptible to positional deviations during the passage through the bridge 9 and to elongation if sticking occurs even to a slightest cut-in portion of the material when severed by a cutter 10.
(3) Prior to wrapping a rubber strip 6 of a predetermined length around the forming drum 2, such has to be passed across a gap for transfer from the belt conveyer 8 to the forming drum 2, so that the rubber strip 6 is likely to deviate again when freed from the transferring surface of the conveyer.
(4) When wrapping the rubber strip around the forming drum 2, the circumferential speed of the drum 2 and the feed speed of the rubber strip 6 by the conveyer 8 have to be in conformity with each other. However, electric control by synchronous motors or the like incurs a problem with regard to the response characteristics at the starting time, and, in a case where the respective drives are synchronized through a mechanical linkage, there arises a need for providing a speed-changing mechanism to cope with variations in the circumferential length of the shaping drum due to use of drums of different sizes. However, commercially available change speed units are unsatisfactory with regard to the rated accuracy and speed, so that there invariably occurs a difference between the circumferential speed of the forming drum and the feeding speed of the cut rubber strip 6, inviting undesirable elongation or wrinkling of the feed material.